5psi is the maximum desired pressure drop across a solenoid valve that is used for compressible fluids such as air.

For EXAIR's standard testing conditions of 80psi and a maximum 5psi pressure drop across a valve, the A constant is 0.048

In sizing a valve to use for a particular application, the valve must have a Cv value equal to or higher than the calculated Cv value based on the required air flow volume, inlet pressure, and pressure drop across the valve.